Plasmacytoid urothelial carcinoma (UC) are luminal tumors with similar immune microenvironment as compared to conventional UC.

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Background:Plasmacytoid urothelial carcinoma (UC) is a rare pathological variant of UC with low chemotherapeutic sensitivity and dismal outcomes. The molecular and immune profiles of such tumors remain poorly investigated. Herein, we investigated the phenotypical features of a cohort of plasmacytoid UC (n = 32) by comparison to a control group of conventional high-grade UC with matched clinicopathological characteristics (n = 30). Methods: Histopathological analysis included the following antibodies: p63, GATA3, CK5/6, CK20 and HER2. In addition, the density of intra-tumor CD8+ lymphocytes, and PD-L1 expression in tumor (TC) and immune cells (IC) were evaluated. Clinical data were collected. Results: Plasmacytoid UC expressed GATA3 (97% vs 86% p = 0.18), CK20 (59% vs 36% p = 0.08) markers and showed a significantly higher rate of HER2 overexpression (2+ and 3+ score: 25% vs 0%, p < 0.01) compared to controls. A significantly lower expression of CK5/6 (22% vs 56%, p < 0.05) and p63 (41% vs 80%, p < 0.05) was observed in plasmacytoid UC compared to controls. The density of tumor-infiltrating CD8+ cells was similar between plasmacytoid and conventional UC (p = 0.5). PD-L1 expression on IC was similar compared to conventional UC (p = 0.3). Overall survival at 5 years was significantly lower among patients with plasmacytoid UC compared to patients with conventional UC (p = 0.02). Conclusions: Together, our study demonstrated that plasmacytoid UC belong to the luminal subtype and display a rather inflamed microenvironment similar to conventional UC. These data support the inclusion of plasmacytoid variant of UC in clinical trials evaluating immune checkpoint inhibitors monotherapy or combination immunotherapeutic strategies.